Polysaccharides have been used as a food raw material from the old time and, in recent years, have begun to be paid attention as a macromolecular material which is environment friendly, as a safe material having biocompatibility and, further, as a functional material. The polysaccharides can be classified into neutral polysaccharides typified by a starch, cellulose, dextrin and the like; acidic polysaccharides typified by alginic acid, hyaluronic acid and the like; and basic polysaccharides typified by chitosan. It has been found that the presence or the absence of an acidic sugar and a basic sugar, and an abundance ratio between them greatly influence on physical properties and function of polysaccharides. Among them, particularly, the acidic polysaccharides have been widely utilized in foods, cosmetics, medicaments and the like, and an acidic polysaccharide having a new structure or function has been expected.
The method which has been previously used for finding a new acidic polysaccharide is a method of finding a novel acidic polysaccharide from nature, or a method of binding a carboxyl group or a sulfuric acid group to an existing polysaccharide by a chemical procedure. However, a uronic acid-containing glucan in which a uronic acid residue is bound to a non-reducing end has not been found in nature and, even if a chemical method is used, synthesis of a uronic acid-containing glucan in which a uronic acid residue is bound only to a non-reducing end is not easy, and, chemical synthesis of a uronic acid-containing glucan in which a uronic acid residue is bound only to a non-reducing end has not been suggested or disclosed.
A procedure of performing a reaction of oxidizing a polysaccharide in the presence of a catalyst of an N-oxyl compound to obtain water-soluble polyuronic acid is known. This oxidation method is to oxidize a polysaccharide while an oxoammonium salt is sequentially produced in a system using an N-oxyl compound such as 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO) and a co-oxidizing agent such as sodium hypochlorite in a water dispersion or solution system of a polysaccharide (Patent Documents 1 to 3). The aforementioned method is applied to hardly-soluble polysaccharides such as cellulose, in addition to water-soluble polysaccharides such as a starch and pullulan. However, in this method, since a glucose residue in the interior of a polysaccharide is randomly oxidized, a polysaccharide containing a glucuronic acid residue only on a non-reducing end cannot be obtained.
As a substance having a glucuronic acid residue on a non-reducing end, various glycosides present in nature such as glycyrrhizin and baicalin, glycosides generated by glucuronic acid conjugation which is performed as detoxification action in a body of an animal, and the like are known. However, these are a so-called glycoside in which glucuronic acid is bound to an aglycon, and do not contain an α(alpha)-1,4-glucan.
α-Glucan phosphorylase (EC2.4.1.1) is an enzyme which acts on glucose-1-phosphate (Glc-1-P) and catalyzes a reaction of transferring a glucose residue to a non-reducing end of a receptor glucan (and a reverse reaction thereof). This reaction is shown in the following formula; wherein, Glucan primer is a receptor glucan, and Glucan Phosphorylase is α-glucan phosphorylase. A glucan obtained by transfer of a glucose residue of one molecule can act again as a receptor, and a transfer reaction is repeated. As a result, the finally obtained glucan can be a high molecular weight glucan.

α-Glucan phosphorylase is one of ubiquitous enzymes which are distributed in almost all organisms, and extremely many kinds of α-glucan phosphorylases are known. α-Glucan phosphorylase, a reaction mechanism of which is best studied, is potato-derived α-glucan phosphorylase.
In recent years, it has been reported that potato-derived α-glucan phosphorylase can use an analog of glucose-1-phosphate (described as G-1-P or Glc-1-P) as a substrate. Non-Patent Document 1 discloses that potato-derived α-glucan phosphorylase can transfer a xylose residue to a non-reducing end of a maltooligosaccharide utilizing xylose-1-phosphate (Xyl-1-P) as a substrate. Non-Patent Document 2 discloses that potato-derived α-glucan phosphorylase can transfer a glucosamine residue to a non-reducing end of a maltooligosaccharide utilizing glucosamine-1-phosphate (GlcN-1-P) as a substrate. G-1-P and a G-1-P analog are shown in the following chemical formula:

On the other hand, Non-Patent Document 3 discloses that glucuronic acid-1-phosphate (GlcA-1-P) being a substance in which a 6-position of glucose-1-phosphate is oxidized can be synthesized by chemical oxidation of glucose-1-phosphate using a TEMPO catalyst. The present inventors tried a few kinds of α-glucan phosphorylases including potato α-glucan phosphorylase, intending that α-glucan phosphorylase is allowed to act on glucuronic acid-1-phosphate to thereby transfer a glucuronic acid residue to a non-reducing end of a receptor glucan, but could not produce an intended glucuronic acid-containing glucan.
A medically effective ingredient of medicaments is rapidly changing from a chemically synthesized stable low-molecular weight compound to an unstable substance which is easily degraded in blood, such as a protein, an antibody and a nucleic acid. For this reason, there is a necessity of stabilizing these unstable medically effective ingredients to keep the blood concentration of the medically effective ingredient high. In addition, in order to decrease side effects of drugs, a necessity of delivering drugs to a target tissue efficiently has been increasing. Under such a background, a so-called drug delivery system (DDS) technique (i.e., a technique of delivering a medically effective ingredient to a desirable target at a desirable concentration for a desirable time) has been utilized in earnest (Non-Patent Documents 4 to 7).
In the DDS technique of medicaments, a modifying material for a medically effective ingredient is important. The term “modifying material” in the present specification refers to a material which modifies a medically effective ingredient by covalently binding, or via non-covalent type interaction, with a medically effective ingredient. By utilizing the modifying material, a variety of properties (for example, pharmacokinetics (for example, absorption, distribution, metabolism and excretion), pharmacological effect, stability and the like) of the medically effective ingredient can be modified. As a substance which has been used previously as the modifying material of the medically effective ingredient, there are a variety of substances, and what is used most generally is a macromolecular material. For example, polyethylene glycol (PEG) which is a synthetic macromolecule, and derivatives thereof are widely utilized as a modifying material for medicaments. Many medicament-modifying materials having a functional group for binding the medically effective ingredient on a terminus of a PEG chain have been developed, and such modifying materials are actually utilized as a medicament. Specific application examples include pegylated interferon α (product name: PEGASYS). Since interferon α has a small molecular weight and is easily excreted into urine, there was a problem that it has a short half-life in blood. However, the half-life in blood was successfully enhanced dramatically by covalently binding interferon α to a PEG chain having a molecular weight of 40,000 to form an interferon α-conjugate having a high molecular weight.
The modifying material of the medically effective ingredient can be utilized not only for directly modifying the medically effective ingredient but also for modifying a finely particulate carrier for other DDSs such as a liposome. An unmodified liposome is captured by phagocyte cells of a reticuloendothelial tissue (RES) during circulation in blood, and the blood concentration of the liposome is rapidly reduced. However, a pegylated liposome in which a PEG chain is bound to a surface of a liposome (also referred to as a Stealth Liposome) is difficult to be taken into the RES, and has a property that it is circulated and stays in blood for a long time. A Stealth Liposome preparation in which doxorubicin being an anti-cancer agent is encapsulated is sold with a trade name of DOXIL (registered trademark) (CAELYX (registered trademark) in Europe). DOXIL (registered trademark) is a liposome having a particle size of 70 to 100 nm, is supplied in the state of a dispersed aqueous solution, and is intravenously administered. There are the results that the disappearance half-life when DOXIL (registered trademark) is administered to a Kaposi's sarcoma AIDS patient is long and about 45 hours, and the concentration in Kaposi's sarcoma after 72 hours from administration is about 5-fold higher as compared with the case of doxorubicin alone.
As described above, the remarkable effect is recognized in the modification of the medically effective ingredient or the finely particulate carrier for DDSs, with a macromolecular material. However, on the other hand, a problem has been pointed out. For example, when a high-molecular weight synthetic macromolecule which has no degradability in a living body and will not undergone renal glomerular filtration is administered to blood, there are a risk that the macromolecule is accumulated in a particular organ and a risk that side effects due to the accumulation are generated. The reason is that a molecule having a molecular weight of a few tens thousands or less present in blood undergoes renal glomerular filtration and is rapidly excreted into urine, but a molecule having a molecular weight of a few tens thousands or more does not undergo renal glomerular filtration and its excretion into urine is limited. For this reason, a modifying material of the medically effective ingredient which can be safely utilized is expected.